Field
The present disclosure relates to a laundry treatment apparatus.
Discussion of the Related Art
A conventional laundry treatment apparatus includes a cabinet defining an external appearance of the apparatus, a tub installed within the cabinet, a drum rotatably installed within the tub such that laundry is washed in the drum, and a motor. The motor includes a rotating shaft which penetrates the tub and is coupled to the drum to rotate the drum.
The drum may fail to maintain dynamic balance because of the position of laundry stored therein, which may cause unintentional rotation of the drum.
Dynamic balance refers to a state of a rotating rotator in which centrifugal force or moment of centrifugal force becomes zero with respect to a rotation axis of the rotator. In the case of a rigid body, dynamic balance is maintained by constant mass distribution about a rotation axis.
Accordingly, with regard to a laundry treatment apparatus, dynamic balance may be understood as the case in which the mass distribution of laundry stored in a drum about a rotation axis of the drum falls within an acceptable range during rotation of the drum (i.e., the case in which the drum is rotated while undergoing vibration within an acceptable range).
On the other hand, failure of dynamic balance (i.e. unbalance) with regard to the aforementioned laundry treatment apparatus refers to a state in which the mass distribution about a rotation axis of the drum is not constant during rotation of the drum. This unbalance occurs when laundry is not uniformly distributed within the drum.
Rotation of the unbalanced drum causes vibration, and in turn noise is generated as vibration of the drum is transmitted to a tub or a cabinet.
Conventionally, to eliminate unbalance of the drum as described above, balancing units have been used in some laundry treatment apparatuses. These balancing units used in conventional laundry treatment apparatuses are of a ball balancer type or a fluid balancer type in which a housing coupled to a drum contains a ball or liquid.
The revolutions per minute of the unbalanced drum reaches a maximum when laundry, which causes the unbalanced state of the drum, passes the lowermost point of the rotation trace of the drum and reaches a minimum when the unbalance inducing laundry passes the uppermost point of the rotation trace of the drum.
Accordingly, the aforementioned ball balancers or fluid balancers used in conventional laundry treatment apparatuses are adapted to control unbalance as the ball or liquid moves toward the lowermost point of the rotation trace of the drum when the unbalance inducing laundry moves toward the uppermost point of the rotation trace of the drum.
Although the above described unbalance control method is available in a steady state in which vibration of the drum falls within a given range, it is impossible to anticipate the large effects of a transient state (i.e., in a transient vibration state) before vibration of the drum reaches the steady state.
Additionally, conventional balancing units have difficulty in actively eliminating unbalance as soon as unbalance occurs.